This section provides background information related to the present disclosure which is not necessarily prior art.
There are an increasing number of electrical actuators in today's vehicles. By way of example and without limitation, electrical actuators may be utilized to power windows, rear-view mirrors, seats, windshield wipers, antennas, spoilers, convertible rooves, hoods, oil pumps, and water pumps. Electrical actuators are driven by electric motors, the size of which is selected according to the torque it must provide to produce the required motion. Thus, if a reasonably high reduction gear ratio can be achieve in a very limited space, smaller and faster electric motors can be used to provide the same level of mechanical power needed for the required motion.
Generally speaking, gear drives used in automotive interior actuators can perform several useful functions: reduce or increase the speed, multiply or decrease the torque, and reverse the direction of rotation. In one example, automotive seat adjuster drives are gear drives that provide seat height adjustment and/or seat tilt position adjustment in automotive vehicles. Automotive seat adjuster drives serve to reduce the electric motor input speed while increasing the input torque. Some of the most important requirements for automotive seat adjuster drives include: the range of reduction ratio, the range of output torque, size, weight, efficiency, the level of noise produced by the automotive seat adjuster drive, shock load capability, cost, durability, and the amount of backlash. For some applications, such as those used in adjusting and maintaining the adjusted position of a vehicle seat, a special requirement called anti-back drive capability is also required. Anti-back drive capability may also be referred to as “non-back drive capability,” “self-locking capability,” or “anti-regression capability.” Gear drives transfer the high speed and low torque rotation of an electric motor input shaft to low speed and high torque rotation of an output shaft, in either, a clockwise (CW) or a counter-clockwise (CCW) direction of rotation. For gear drives with anti-back drive capability, any attempt to transfer torque from the output shaft back to the input shaft by applying an external load (e.g. occupant weight or external reaction forces in the case of a crash accident, etc.) to the output shaft is prevented. This protects against damage to the electric motor and ensures that the vehicle seat maintains its position when the electric motor is not energized.
Gear drives with anti-back drive capabilities have been developed that multiply the torque and reduce the speed in either a clockwise or a counter-clockwise direction of rotation. Worm and worm-wheel gear drives have been used successfully for many years as a safety or self-locking device. Worm and worm-wheel gear drives avoid the need for an external brake or clutch mechanism. However, the disadvantages of worm and worm-wheel gear drives are that the anti-back drive capability is achieved only if the reduction ratio is on the order of 25:1 or larger, leading to a relatively low mechanical efficiency. Theoretically, the maximum efficiency of worm and worm-wheel gear drives with anti-back drive capability is 50 percent. Moreover, worm and worm-wheel gear drives may not provide anti-back drive capability in all operating conditions, such as in the presence of unwanted dynamic vibrations.
In addition to anti-back drive capability and an increased operating efficiency, gear reduction mechanisms used in vehicle seat height and tilt adjusters must have: a relatively high gear ratio, (typically in the range of 300:1 to 700:1), reduced packaging, reduced noise during operation, and low manufacturing and assembly costs. A practical solution for a coaxial or an orthogonal gear transmission that is able to meet all the above mentioned requirements using only a single-stage reduction mechanism is not possible. Thus, several gear drives are being pursued that utilize two-stages of gear reduction, in which the second-stage of gear reduction provides the necessary output torque and speed while preserving anti-back drive capability. Usually, such two-stage transmissions exploit the properties of single-stage planetary gear drives, which use an eccentric to drive a planetary gear for providing high gear ratios in a very compact space, and different coupling or compensating arrangements to prevent rotation of the planetary gear about its own axis of rotation to provide anti-back drive capability. Such coupling or compensating arrangements are based on a reciprocating sliding, rolling, or wedging action between the planetary gears and the housing or another component that is fixed to the housing.
The following patents and patent application publications EP0450324, U.S. Pat. No. 4,228,698, WO2012/150050, US2013/0180348 and US2007/0209857 disclose planetary gear reduction mechanisms where the coupling or compensating arrangements use reciprocating, sliding movements between adjacent elements during torque transmitting operations. Several other patents, including U.S. Pat. No. 5,425,683, U.S. Pat. No. 6,261,199, U.S. Pat. No. 3,013,447, U.S. Pat. No. 2,609,713, FR679410, U.S. Pat. No. 2,508,121, U.S. Pat. No. 2,995,226 and U.S. Pat. No. 4,967,615 disclose planetary gear reduction mechanisms where the coupling or compensating arrangements use rolling contact action between adjacent elements during torque transmitting operations. Although all of the aforementioned patents and patent application publications solve the main requirement related to anti-back drive capability, these solutions exhibit low overall mechanical efficiency, require a large packaging space, utilize heavy and complicated architectures, produce excessive noise, and/or are expensive to manufacture and assembled.